mass spectrometry

mass spectrometry
Name	Mass spectrometry
Caption	A simplified schematic of a typical instrument
Acronym	MS
Classification	Analytical chemistry
Related	Chromatography, Spectroscopy
Manufacturer	Thermo Fisher Scientific, Agilent Technologies, Waters Corporation, Bruker Corporation, Shimadzu

mass spectrometry is an analytical technique that measures the mass-to-charge ratio of ions to identify and quantify molecules in a sample. The fundamental process involves converting sample molecules into gas-phase ions, separating these ions based on their dynamic properties in electric and magnetic fields, and detecting them to produce a mass spectrum. This spectrum provides critical information about the molecular weight, structure, and composition of the analyte, making the technique indispensable across numerous scientific fields from pharmaceuticals to space exploration.

Principles and theory

The core principle is based on the motion of charged particles in electromagnetic fields, governed by the Lorentz force law. Ions are formed from the sample, accelerated, and their trajectories are controlled by fields within a vacuum system. The resulting separation allows the determination of the mass-to-charge ratio (m/z). The underlying theory connects directly to fundamental physics, including concepts from classical mechanics and electromagnetism. The data output, a mass spectrum, plots ion signal intensity against m/z, where patterns reveal isotopic distributions, as seen with elements like carbon-13, and provide a unique fingerprint for chemical identification.

Instrumentation

A standard instrument consists of several key modules: an ion source, a mass analyzer, and an ion detector, all maintained under high vacuum by pumps like turbomolecular pumps or diffusion pumps. The sample introduction system varies, often interfaced with techniques like gas chromatography or liquid chromatography. The detector, frequently an electron multiplier or a Faraday cup, converts the ion current into an electrical signal. This signal is processed by a data system, typically a computer running software from vendors such as Thermo Fisher Scientific or Waters Corporation, to produce the final spectrum. The entire apparatus requires precise engineering, as pioneered by companies like PerkinElmer and Varian, Inc..

Ionization techniques

The method of converting neutral molecules into ions is critical and depends on the sample's nature and volatility. Electron ionization, developed alongside early work at the University of Cambridge, is robust for small, volatile organics. Electrospray ionization, pioneered by John B. Fenn at Yale University, gently ionizes large biomolecules like proteins and is central to proteomics. Matrix-assisted laser desorption/ionization, co-invented by Koichi Tanaka of Shimadzu and Franz Hillenkamp at the University of Münster, is vital for analyzing polymers and biomolecules. Other methods include chemical ionization, atmospheric pressure chemical ionization, and inductively coupled plasma ionization, the latter being the standard for elemental analysis in geochemistry.

Mass analyzers

These components separate ions by their m/z. The quadrupole mass analyzer, a common design used by Agilent Technologies, filters ions using oscillating electric fields. The time-of-flight analyzer, used in instruments from Bruker Corporation, measures the time ions take to drift through a field-free region. The ion trap, including the Paul trap and the Orbitrap invented by Alexander Makarov at Thermo Fisher Scientific, confines ions in orbital motions. High-resolution measurements are achieved with sector instruments, like those historically built by Finnigan Corporation, and Fourier-transform ion cyclotron resonance cells, advanced in work at the National High Magnetic Field Laboratory.

Tandem mass spectrometry

Often abbreviated as MS/MS, this involves multiple stages of mass analysis, usually separated by a collision cell. In a common sequence, a precursor ion is selected by a first analyzer, fragmented through processes like collision-induced dissociation with an inert gas such as argon, and the resulting product ions are analyzed by a second mass analyzer. This provides structural information. Common instrument configurations for this include the triple quadrupole, the quadrupole-time-of-flight, and the ion trap-Orbitrap hybrid. The technique is foundational in structural elucidation and quantitative analysis, heavily utilized in laboratories like those at the Mayo Clinic and the Broad Institute.

Applications

The technique has transformative applications across science and industry. In biochemistry and medicine, it is used for drug discovery by companies like Pfizer, clinical diagnostics for conditions like inborn errors of metabolism, and proteomics research at institutions like the Scripps Research Institute. In environmental science, it monitors pollutants and pesticides for agencies like the Environmental Protection Agency. It ensures food safety, detecting contaminants for the Food and Drug Administration, and is used in forensics for toxicology screening. In space science, instruments on missions like Cassini–Huygens and the Mars Curiosity rover have analyzed extraterrestrial atmospheres and soils.

Category:Analytical chemistry Category:Laboratory techniques Category:Spectroscopy